1. Field of the Invention
The present invention relates to an inflator that generates inflation gas for inflating an airbag, and more particularly, relates to a pyrotechnic inflator that stores two kinds of gas generating charges that have different combustion speeds.
2. Description of Related Art
An inflator provided with two gas generating charges of different speeds of combustion is known in JP2002-283942 (FIG. 4). The inflator includes two combustion chambers partitioned by a bulkhead, a first gas generating charge of fast combustion speed, a second gas generating charge of slower combustion speed relative to the first, the charges being stored respectively in the two combustion chambers, and an ignition device for igniting the first gas generating charge.
This inflator is provided at part of the bulkhead between the two combustion chambers a portal through which a flame generated due to combustion of the first charge propagates to the second charge. With this arrangement, only a part of the second generating charge burns firstly, and it takes a long time for an entire second charge to be ignited. This may result in failure to obtain a sufficient amount of inflation gas immediately after initiation of actuation of the inflator (i.e., in the initial stage of actuation of the ignition device).
The reference referred to above also discloses in FIG. 3 an inflator wherein first and second gas generating charges are stored in a combustion chamber in a mixed fashion.
With this inflator, the first and second gas generating charges initiate combustion at the same time when the ignition device is actuated. However, if the second charge surrounds the first charge due to oscillation of a vehicle and, the like, it is likely that combustion of the second charge hinders quick combustion of the first charge. This may make it difficult to obtain a sufficient amount of inflation gas by combustion of the first charge immediately after actuation of the inflator. Moreover, oscillation of a vehicle and the like makes it difficult to keep the first and second gas generating charges in a steady, desired mixed condition in the combustion chamber. Therefore, it is difficult to guarantee steady performance for every inflator.